1. Field of the Invention
The present invention relates to a semiconductor device of so-called chip-on-chip structure.
2. Description of Related Art
Semiconductor devices of chip-on-chip structure have been proposed, which include a first semiconductor chip (primary chip) and a second semiconductor chip (secondary chip) bonded onto the first semiconductor chip, for example, with its face down. In this case, electrical connection between the first and second semiconductor chips is achieved by bonding bumps provided on the respective chips in opposed relation. For external connection after the chip-on-chip structure is sealed in a package such as of a resin, wire-bonding between terminals of a lead frame and external connection pads of the first semiconductor chip is performed. The first semiconductor chip is die-bonded to an island of the lead frame.
In the chip-on-chip semiconductor device, the primary chip and the secondary chip are disposed in close proximity to each other. Therefore, a radiation noise from one of the chips may deteriorate the operating characteristics of the other chip.
Where the second semiconductor chip of the chip-on-chip semiconductor device serves as a driver circuit incorporating a bipolar transistor or as a flash memory circuit with high power consumption and with high heat release, the heat dissipation through the lead frame is insufficient. This may deteriorate the operating characteristics of the second semiconductor chip and, in addition, the heat from the second semiconductor chip may adversely affect the first semiconductor chip. Therefore, the semiconductor device may fail to properly maintain its operating characteristics as a whole.
It is a first object of the present invention to provide an improved semiconductor device of chip-on-chip structure in which a radiation noise generated by one chip is prevented from affecting the other chip.
It is a second object of the invention to provide a semiconductor device of chip-on-chip structure with a consideration for heat dissipation.
A semiconductor device according to a first aspect of the invention comprises a first semiconductor chip, a second semiconductor chip bonded onto the first semiconductor chip in stacked relation, and a noise shield film provided between the first semiconductor chip and the second semiconductor chip for preventing the first and second semiconductor chips from being mutually influenced by noises thereof.
With this arrangement, the noise shield film is provided between the first semiconductor chip and the second semiconductor chip. Therefore, the chip-on-chip semiconductor device can prevent a radiation noise generated by one of the chips from adversely affecting the operating characteristics of the other chip.
The semiconductor device preferably further comprises a connection mechanism which connects the noise shield film to a power supply portion (a power supply line or a ground line). That is, the noise shield film is connected, for example, to a supply potential portion or a ground potential portion of the lead frame via a bonding wire, whereby the noise shield film can assuredly provide a noise shield effect.
The noise shield film is preferably a metal film provided on a surface of the first semiconductor chip and/or the second semiconductor chip, the metal film being formed of the same metal material as bumps which are to be used for bonding the first and second semiconductor chips to each other. In this case, formation of the noise shield film can be achieved simultaneously with formation of the bumps. Since the semiconductor chips typically each have a surface protective film formed on the outermost surface thereof, the noise shield film is preferably provided on the surface protective film.
Where the first semiconductor chip is greater in size than the second semiconductor chip, the noise shield film may be provided at least on the first semiconductor chip for easy connection of the noise shield film to the lead frame or the like.
The noise shield film is preferably provided in a region which covers a major noise source. Where the major noise source is present in the second semiconductor chip and the first semiconductor chip is greater in size than the second semiconductor chip, for example, the noise shield film may include a shield portion which covers an area of the second semiconductor chip where the major noise source is present, and an extension portion extending outwardly from the shield portion on the surface of the first semiconductor chip.
The first and second semiconductor chips may be bonded to each other with active surfaces thereof being opposed to each other.
A semiconductor device according to a second aspect of the invention comprises a first semiconductor chip, a second semiconductor chip bonded onto the first semiconductor chip in stacked relation, a heat conductive member provided between the first semiconductor chip and the second semiconductor chip to define a heat release path for releasing heat generated by the second semiconductor chip, and a connection member thermally connecting the heat conductive member to a heat radiator.
With this arrangement, the heat generated by the second semiconductor chip is transferred to the heat radiator by conduction through the heat conductive member provided between the first and second semiconductor chips and the connection member. The semiconductor device of chip-on-chip structure is thus given a consideration for heat dissipation and, even if the second semiconductor chip generates a great amount of heat, the semiconductor device can properly maintain its operating characteristics as a whole. That is, the heat dissipation from the second semiconductor chip can advantageously be achieved, so that the operating characteristics of the second semiconductor chip can properly be maintained. Further, there is no possibility that the first semiconductor chip is adversely affected by the heat generated by the second semiconductor chip.
The heat radiator maybe a heat sink. In this case, the connection member may be a bonding wire which connects the heat sink to the heat conductive member.
The heat conductive member is preferably composed of a metal (e.g., gold) having a high heat conductivity.
The heat conductive member may be a metal film provided on a surface protective film of at least one of the first semiconductor chip and the second semiconductor chip. Where the first semiconductor chip and the second semiconductor chip are respectively formed with such metal films, the metal films are disposed in contact with each other or bonded to each other, and the metal film provided on the first semiconductor chip is thermally connected to the heat radiator via the connection member such as the bonding wire.
Where the metal film provided on the surface of the first semiconductor chip and/or the second semiconductor chip serves as the heat conductive member, the metal film is preferably formed of the same material (e.g., gold) as bumps which are to be provided on the surface of the first and/or second semiconductor chip. Thus, the metal film can be formed as the heat conductive member on the surface protective film simultaneously with formation of the bumps.
It is preferred that the first semiconductor chip is greater in size than the second semiconductor chip and the metal film has an extension portion which extends from the vicinity of a heat source of the second semiconductor chip to a region of the first semiconductor chip not covered with the second semiconductor chip. In this case, the extension portion of the metal film may thermally be connected to the heat radiator via a bonding wire or the like.
The first semiconductor chip and the second semiconductor chip are preferably bonded to each other with active surfaces thereof being opposed to each other. In this case, the bumps are usually provided on the active surfaces of the first and second semiconductor chips. Therefore, the metal films can be formed on the surfaces of the respective chips in the bump formation process. Thus, the metal films on the respective chips can be brought into contact with each other or bonded to each other when the first and second semiconductor chips are joined together.
The first semiconductor chip is preferably die-bonded to a lead frame. Thus, heat dissipation of the first semiconductor chip can advantageously be achieved through the lead frame.